Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Water Bridge and Weight
Name: Aal
Status: Other
Grade: Other
Location: NJ
Country: United States
Date: November 2007

When designing a water bridge, does the bridge have to be designed to withstand the additional weight of ship and barge traffic, or just the weight of the water?

Hi Aal,

In a water bridge, such as the amazing one that was recently opened in Germany shown in the photo here...

...the bridge only needs to withstand the weight of the water. This is because when a boat floats on water, it displaces its own weight of water. That means, that the volume of water that the hull replaces, weighs exactly as much as the boat does. The water that the hull displaces, is replaced by a boat that weighs exactly as much as the water used to.


Bob Wilson

The simple answer is that no, a ship will simply displace its own weight of water and no extra weight needs to be supported by the bridge.

Engineering structures are designed typically with many other considerations in mind besides the normal weight to be carried. For example, structures typically have a "safety factor." A safety factor of three, for example, means that the structure will actually support three times the design load without actually failing. Other important considerations for bridges (and buildings) are wind loading and earthquakes. So a full answer to this question would require the expertise of a civil engineer familiar with such projects.

Robert Erck

Click here to return to the Engineering Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory